Laser-induced breakdown spectroscopy (LIBS) has been widely investigated in recent decades for different applications ranging from space exploration to biological specimens. In particular, LIBS can be used in methods to identify biomarkers, such as for diseases such as cancer, present in a biological sample, such as a bodily fluid, by reacting the biomarker with a plurality of element-coded particles each comprising a compound, such as a protein, oligonucleotide, polysaccharide, or lipid, that binds to the biomarker, removing unbound element-coded particles from the sample, detecting the element-coded particles in the sample using a laser-induced breakdown spectrometer, and quantifying the element coded particles in the sample, such as pursuant to the methods described in U.S. Published Pat. App. No. US 20110171636, titled “Mono- and multi-element coded libs assays and methods,” listing the present inventor as a co-inventor and incorporated herein in its entirety by reference.
The success of LIBS is due to a set of advantages that makes this analytical technique unique such as multi-element analysis, fast response, remote sensing, little to no sample treatment, the attractive cost of the instrumentation, and its ease of use. Although LIBS was born as a field technique, the improvement in instrumental capabilities and knowledge on fundamental aspects of laser-induced plasma spectroscopy has allowed for a large expansion into laboratory applications. As a result, LIBS is now competing with other conventional laboratory techniques, still holding some of the advantages mentioned above, but at the same time the analytical performance (i.e., accuracy, and laser shot-shot reproducibility) could be improved in order to really be competitive with other well-established techniques. As with any ordinary analytical tool, the laboratory setting introduces the possibility of tighter control of LIBS experimental conditions and the use of more sophisticated analysis protocols and sample treatment.
One of the most widely cited advantages of laser-induced breakdown spectroscopy (LIBS) is that it does not require sample preparation, but this may also be the biggest factor holding it back from becoming a mature analytical technique like LA-ICP-MS, ICP-OES, or XRF. In general, LIBS performance may be enhanced using two main approaches: a) improving the plasma emission signal and b) modifying the specimens. Until now the LIBS community has primarily focused its efforts on enhancing the plasma emission, which tends to increase cost by adding components (e.g., additional lasers, high performance detectors) and calls for specific expertise in the fields of plasma physical chemistry and laser technology. This approach may not meet the requirements of scientists and operators who want to use LIBS in the same ways as they would use any other classical analytical tool. The manipulation of specimens to make them more suitable for laser ablation and LIBS is gaining interest for two reasons. First, to decrease the limits of detection (LOD) in already established LIBS applications and second, to expand the capability of LIBS to those applications where heterogeneity and/or matrix effects had limited its use. The operational cost of sample treatment can be weighed against the advantage of applying LIBS analysis instead of another analytical technique, keeping in mind that most conventional analytical techniques inherently require significant manipulation of specimens to achieve good results.
While there are certain specimen types that are prone to yield excellent LIBS results without any sample treatment (mostly homogeneous solids such as metals, glass, and polymers), the possible applications of LIBS have been greatly expanded through the use of sample preparation techniques that have resulted in analytical performance (i.e., limits of detection, accuracy, and repeatability) on par with XRF, ICP-OES, and often ICP-MS.
Many LIBS researchers have developed, adapted, and improved upon sample preparation techniques for various specimen types in order to improve the quality of the analytical data that LIBS can produce in a large number of research domains. See, e.g., Sarah C. Jantzi et al., “Sample treatment and preparation for laser-induced breakdown spectroscopy,” Spectrochimica Acta Part B Atomic Spectroscopy, November 2015, co-authored by the present inventor, and incorporated herein by reference.
Despite the many techniques developed, there is still a need in the art to develop sample preparation techniques that take into account how laser energy affects material ejection and, in turn, ablation efficiency. In particular, use of LIBS systems to analyze liquids, solutions and slurry samples or mixtures thereof may cause laser induced splashing from the liquid sample, making it hard to obtain accurate qualitative and quantitative analysis of the samples. Accordingly, there is a particular need in the art for improved sample preparations techniques for “liquids” or “fluid samples,” which terms as used herein, except when apparent to the contrary, refer without limitation to any samples comprising at least a liquid fraction, and which may or may not also contain soluble or insoluble components therein.